What we do
Our laboratory studies how biologically-produced molecules can carry information about living organisms, and preserve this information in the sedimentary and geological records. We examine the structures, sequences, and isotopic content of information-containing molecules.
DNA is the biomolecule responsible for encoding heritable information, and encodes genes that can be expressed by an organism. Its information content is high, but its preservation potential is relatively low; under ideal conditions it may be preserved in environments for a few thousands or tens of thousands of years. Genomic DNA sequences are increasingly stored in databases such as GenBank. These databases may be queried for genes encoding proteins carrying out functions such as the synthesis of lipids - if the genes are known!
RNA is synthesized during gene expression. It is also used to build the ribosome. Like DNA, it contains sequence information, but it also carries information about the expression level of each gene. However, RNA is very unstable and is rarely preserved in the environment for more than a few minutes.
Protein is constructed of sequences of amino acids and is the major building block of enzymes. Amino acid sequences contain information, although less than DNA or RNA. It also contains expression information that can be preserved over moderate timescales: at least as long as DNA, and possibly much longer.
Lipids don’t carry as much information as DNA, RNA, or protein. Unlike these other molecules lipids are not information-encoding polymers. However, they still contain information, since a lipid’s structure informs us about the genes that were required for its synthesis. For instance, more than a dozen genes are involved in the synthesis of cholesterol. Thus, the detection of cholesterol indicates the presence of organisms with these genes. The carbon and hydrogen in lipids (as in DNA, RNA, and protein) also contains isotopic information that can tell us about the physiology of the organism from which it derives, and perhaps something about its environment. But most importantly, lipids are stable: they can be preserved in rocks for billions of years.
Inorganic compounds involved in biogeochemical cycles can also carry information. For example, some microorganisms gain energy by converting sulfate to sulfide. This conversion partitions the isotopes of sulfur and oxygen between sulfate and sulfide, and the resulting isotope ratios can be measured in sulfate- and sulfide-containing rocks. By understanding how biology partitions isotopes, we might better interpret information in the rock record.
The study of these molecules in modern environments, in the laboratory, and in ancient rocks can help to answer questions related to the coevolution of life and the Earth. What were ancient ecosystems like? What were the first metabolic cycles? How can we better understand the evolutionary history of microbial life? What molecular and isotopic records are preserved in the rock record, and how can we interpret them? How do lipids preserve information about environmental parameters such as temperature? How has the Earth’s carbon cycle changed over geologic time, and what are the important contributions to it? Our investigations into biogeochemistry seek to answer questions like these.